1. Field of the Invention
The present invention relates to a method for making a fine annular charge storage electrode in a semiconductor device, and more particularly to a method for easily forming a charge storage electrode having a high capacitance and fine annular patterns, using a phase-shift mask.
2. Description of the Prior Art
In recent years, the development of semiconductor devices in which numerous elements are integrated at a high density on a semiconductor chip has been actively under way. For the memory cell of the dynamic random access memory(DRAM), there have been proposed various structures suitable for miniaturization of the device.
Furthermore, to obtain a sufficient capacitance corresponding to decrease of cell are a in a high density device, a device with trench, fin and cylinder-shaped structures has been developed, and ferroelectric materials, such as TaO.sub.5 whose dielectric constant is larger than that of the ONO(Oxide-Nitride-Oxide) layer, have been developed. That is to say, modifications of structures of charge storage electrodes and dielectric materials, having a high capacitance, have been developed.
In a conventional method for forming a charge storage electrode in a semiconductor device, the patterns for forming the charge storage electrodes are formed with chromium patterns on a quartz substrate. Accordingly, one chromium pattern formed on the photomask corresponds to one photoresist pattern. Then, to form a charge storage electrode having a cylinder-shaped structure, several lithography processes and etching processes are desired. However, the photomask having chromium patterns, which perfectly intercept the light, can not form charge storage electrodes having a sufficient capacitance, since chromium patterns can not form fine patterns which are smaller than the wavelength from the light source. Also, in formation of the charge storage electrode having the cylinder-shaped structure, although single cylinder structures or more have been developed, it is very difficult to obtain sufficient capacitance, so that there have been many problems in high density devices.